1. Field of the Invention
The present invention relates to a cyclopentaphenanthrene-based compound and to an organic electroluminescent device using the same. More particularly, the present invention relates to a cyclopentaphenanthrene-based compound and to an organic electroluminescent device including an organic layer made of the cyclopentaphenanthrene-based compound.
2. Description of the Related Art
Organic electroluminescent (EL) devices (also referred to as organic light-emitting devices) are active emission display devices that emit light by recombination of electrons and holes in a thin layer (hereinafter, referred to as “organic layer”) made of a fluorescent or phosphorescent organic compound when a current is applied to the organic layer. The organic EL devices have advantages such as lightweight, simple constitutional elements, easy fabrication process, superior image quality, and wide viewing angle. In addition, the organic EL devices can perfectly create dynamic images, achieve high color purity, and have electrical properties suitable for portable electronic equipment due to low power consumption and low driving voltage.
Eastman Kodak Co. developed an organic EL device of a multi-layered structure using an aluminum quinolinol complex layer and a triphenylamine derivative layer (U.S. Pat. No. 4,885,211), and an organic EL device including an organic light-emitting layer made of a low molecular weight material capable of covering a broad emission wavelength range from UV to visible light (U.S. Pat. No. 5,151,629).
Light-emitting devices are self-emission devices and have advantages of a wide viewing angle, good contrast, and rapid response speed. The light-emitting devices can be classified into inorganic light-emitting devices including a light-emitting layer made of an inorganic compound and organic light-emitting devices (OLEDs; also referred to as “organic electroluminescent devices” (organic EL devices)) including a light-emitting layer made of an organic compound. The OLEDs show better brightness, driving voltage, and response speed characteristics and can achieve polychromatic changes, compared to inorganic light-emitting devices, and thus there have been many researches about OLEDs.
Generally, OLEDs have a stacked structure of an anode, an organic light-emitting layer, and a cathode. OLEDs may also have various structures such as anode/hole injection layer/hole transport layer/light-emitting layer/electron transport layer/electron injection layer/cathode or anode/hole injection layer/hole transport layer/light-emitting layer/hole blocking layer/electron transport layer/electron injection layer/cathode.
A material used in OLEDs can be divided into a vacuum deposition material and a solution coating material according to a method of forming an organic layer. The vacuum deposition material must have a vapor pressure of 10−6 torr or more at 500° C. or less, and may be a low molecular weight material with a molecular weight of 1200 or less. The solution coating material must have high solubility in a solvent to prepare a solution, and mainly includes an aromatic or heterocyclic compound.
In the case of manufacturing an OLED using a vacuum deposition process, manufacturing costs increase due to the use of a vacuum system. In the case of using a shadow mask to form pixels for a natural color display, it is difficult to obtain high resolution pixels. On the other hand, in the case of manufacturing an OLED using a solution coating process such as inkjet printing, screen printing, or spin coating, manufacturing is easy, manufacturing costs are low, and a relatively good resolution can be achieved as compared to the case of using a shadow mask.
However, thermal stability, color purity, etc. of light-emitting molecules of materials that can be used in the solution coating process are inferior to those that can be used in the vacuum deposition process. Even when the light-emitting molecules of the materials that can be used in the solution coating process are excellent in thermal stability, color purity, etc., the materials may be crystallized to grow a crystal size corresponding to a visible light wavelength range after they are made into an organic layer, thereby scattering visible light, resulting in turbidity phenomenon, and pin holes may be formed, thereby causing device degradation.
Japanese Patent Laid-Open Publication No. 1999-003782 discloses an anthracene compound substituted by two naphthyl groups which can be used in a light-emitting layer or a hole injection layer. However, the anthracene compound has poor solubility in a solvent, and an OLED using the compound exhibits unsatisfactory characteristics.
Therefore, there is still need to develop an organic EL device having improved driving voltage, brightness, efficiency and color purity, and good thermal stability.